3rd generation (3G) systems, such as the Universal Mobile Telecommunication System (UMTS) have been developed and deployed to further enhance the communication services provided to mobile users compared to those communication services provided by the 2nd generation (2G) communication system known as the Global System for Mobile communication (GSM).
High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA) have been developed to optimise UMTS with increased data rate and capacity for packet data services in downlink and uplink, respectively. HSDPA and HSUPA are referred together as High Speed Packet Access (HSPA). Standards for HSPA have been established within the Third Generation Partnership Project (3GPP): HSDPA was introduced as a release 5 feature in 3GPP and HSUPA was introduced in release 6. Within 3GPP release 7, further improvements to HSPA have been specified in the context of HSPA+ or HSPA evolution.
As is well known, cellular communication systems, such as UMTS, provide communication to mobile devices via a plurality of cells, with each cell served by one or more base stations. The base stations are interconnected by a radio network controller which can communicate data between the base stations. A mobile device communicates via a radio communication link with a base station of the cell within which the mobile station is situated. In UMTS, the base stations which are part of the UTRAN are known as Node Bs and a mobile device is known as User Equipment (UE).
3GPP release 7 introduced Continuous Packet Connectivity (CPC) which is aimed at providing improved user experience. For example, CPC allows a UE to stay connected over longer periods and so avoids frequent connection termination and re-establishment, even though the UE may only occasionally have active periods of data transmission, but which has features to reduce the uplink and downlink control channel overhead. These features include Uplink Discontinuous Transmission (DTX) for reducing uplink control channel overhead and Downlink Discontinuous Reception (DRX) for reducing downlink control channel overhead.
Release 7 (and release 8) also introduced Circuit Switched (CS) voice services over HSPA so as to improve the system capacity for voice and data services using the improvements provided by the HSPA radio interface while still employing the current voice core networks. The voice traffic is carried over the HSPA radio channels but the voice traffic is not carried over an IP backbone. In order to implement CS over HSPA, minor changes are required to the UTRAN and the UE, which may be implemented through software upgrades.
One of the requirements for the network to configure the UE with DTX/DRX parameters for CPC is the capability of the UE to support high speed channels both in the uplink and downlink. In the case of CS over HSPA, the voice call is carried by HSDPA and HSUPA packets allowing DTX/DRX modes to be used in the UE to reduce RF activity.
The network configures the UE with DTX/DRX parameters which allow the UE to enter the DTX and DRX modes and which define the patterns or cycles of the DTX and DRX modes.
There are several parameters associated with the DRX mode including the DRX cycle parameter and the ‘Inactivity Threshold for DRX’ parameter. The DRX cycle parameter defines the cycle or pattern of the normal DRX mode and indicates the subframe of the High Speed Shared Control Channel (HS-SCCH) the UE is required to monitor for possible downlink data allocations. For example, if the DRX cycle parameter is 5, the UE only monitors the HS-SCCH on every 5th subframe. By limiting the number of subframes to be monitored by the UE, the battery consumption of the UE can be reduced. The ‘Inactivity Threshold for DRX’ parameter indicates the number of subframes of the High Speed Shared Control Channel (HS-SCCH) the UE is required to monitor following reception of a data packet. If there is no data scheduled for the UE in this period, as determined from monitoring the HS-SCCH, the UE enters DRX mode and follows the pattern or cycle of the normal DRX mode (which is defined by DRX cycle parameter). When the UE is scheduled a packet during a DRX cycle while monitoring HS-SCCH, it continues to monitor HS-SCCH again for ‘Inactivity Threshold for DRX’ subframes before entering the normal DRX mode.
In a voice call, when one person is talking, the other user is typically listening which means that the UE of the user talking typically receives Silence Insertion Descriptor (SID) packets from the UE of the ‘listening’ user. Upon reception of a SID packet, the UE, based on the above procedure for CPC, is required to monitor HS-SCCH for ‘Inactivity Threshold for DRX’ subframes irrespective of what other services the UE is receiving or is involved in. This may cause unnecessary current drain in the UE. Since voice continues to be a primary application for mobile telephony, this can cause quite a significant drain in battery of the UE.